Conditioned taste aversion (CTA) is a robust learning experience in which an animal made sick after exposure to a novel taste avoids the same taste in the future. I will use the known time course and well- defined circuitry for this behavior to probe for differentially expressed genes underlying a mechanism for encoding memory, using DNA microarray hybridization. I will test explicitly the hypothesis that this type of learning involves microanatomical plasticity of brain circuitry, but will collect data that could point to alternative mechanisms as well. In Phase I, candidate genes for involvement in CTA formation will be identified and distinguished according to their non-specific association with different stimulus and response elements of the behavior, or with formation of the contingent response itself. In Phase II, selective lesioning and time course experiments will be used to strengthen the relationship between the candidate genes and the learning task. In Phase III, differential expression of candidate genes will be verified and localized by in situ hybridization. This study makes a novel contribution to research on learning and memory by applying a new and powerful technology that has the potential for revealing an unprecedented number of parallel and sequential events underlying memory formation at the molecular level in a single series of experiments. As such, it represents a more realistic view of the way in which a system as complex as the brain likely processes and encodes experiential information.